**2.2. Somaclonal variations**

Somaclonal variation have been employed to improve cane-quality, sugar recovery, yield, drought tolerance and disease resistance. To increase the incidence of genetic variation and to get positive modifications in the target plant genome, physical (ion beams, gamma rays) and chemical (sodium azide, sodium nitrite and ethylmethane sulfonate (EMS) mutagens have been tested [15]. Introduction of selection pressure at cellular level has been successful to isolate mutants with desired characters. For fungal pathogen resistance inoculation with fungal pathotoxins or culture filtrates has been very effective. Somaclonal variants of sugarcane were developed against eye spot disease by Larkin and Scowcroft. Mutagenesis has been used by various researchers to isolate embryogenic cells and plants tolerant against red rot [16].

Similarly, for abiotic stress tolerance polyethylene glycol, mannitol and sodium chloride has been used for the selection of plants against drought/salinity tolerance [17]. Various studies were conducted to evaluate the level of variability and transmission of variations into the next generation by vegetative propagation. These studies verified the occurrence of considerable variations in *in-vitro* derived plants. However, extensive field experiments showed that tissue culture derived phenotypic variations were often temporary as most of the variants relapsed to the parental phenotype in the first ratoon crop [18]. Few other studies also supported somaclonal variations but to little extent. Chowdhury and Vasil [19] were not able to recognize any considerable variation in the DNA of plants regenerated from cell suspension, protoplasts and callus cultures. Taylor et al. [20] performed random amplified polymorphic DNA (RAPD) analyses of plants regenerated from embryogenic culture. Only a few polymorphisms were observed. Anyhow, there are different opinions about the somaclonal variations and their transmission to next generation. Most of the researchers are of the view that these variations depend upon the genetic makeup and experimental conditions under which plants are screened and selected.
